Method of producing a hollow poppet valve and an apparatus therefor

ABSTRACT

A method of producing a hollow valve comprises the step for forming material having a blind hole along its axis, the step for extruding the material in a shaping hole in a die downward and the step for lowering a lower part of a pin to an upper part of a smaller-diameter portion of the shaping hole to allow the material to plastically flow downward through a gap between the lower part of a pin and the smaller-diameter portion of the shaping hole thereby molding a primary intermediate of the hollow valve having a stem and a head at the upper end of the stem through which a hole is formed.

BACKGROUND OF THE INVENTION

The present invention relates to a method of producing a hollow poppet valve for an internal combustion engine and an apparatus therefor.

A poppet valve used in an internal combustion engine particularly for an automobile is hollow or includes metallic sodium in a cavity.

In JP63-109205A, a method of producing a hollow valve comprises the step for molding a valve in which a stem has a head at one end by hot forging from material in which a core is disposed in the center; the step for pulling out the core to form a cavity along its axis; and the step for closing the cavity with a closure. JP7-119421A discloses that material which includes a core in a cavity along its axis is molded by hot forging to a valve having a head at one end. Metallic sodium is enclosed in the cavity and an open end is closed with a closure. JP7-119421A also discloses that material which includes a core in a cavity along its axis is forged with heat to mold a valve having a head at one end of a stem. Then the core is bored with a gun drill to form a cavity along its axis, and metallic sodium is inserted in the cavity, and a closure is fixed to an open end of the stem. JP4-334708A discloses that a valve is bored along its axis with a gun drill to form a cavity.

The method of producing a hollow valve comprises at least four steps comprising the step for making the core; the step for forming the cavity for the core in the material; the step for inserting the core into the cavity; and the step for pulling out the core, thereby decreasing the productivity and increasing the producing cost.

In JP7-119421A and JP4-334708A, the boring for forming the cavity with the gun drill takes a long time and decreases its productivity. The short life of the drill increases its producing cost.

Austenite heat-resistant steel for an exhaust valve is hard and it is very difficult to shave the steel. To bore the steel makes its life decreased.

SUMMARY OF THE INVENTION

In view of the disadvantages in the prior art, it is an object of the invention to provide a method of producing a hollow poppet valve that has a cavity along its axis at low cost efficiently.

It is another object of the invention to provide an apparatus for producing the hollow poppet valve.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described, by way of example only, with reference to the attached drawings, wherein:

FIG. 1 is a view showing one embodiment of the steps of a method of producing a hollow valve according to the present invention.

FIG. 2 is a central vertical sectional front view of a first press for molding a primary intermediate of the hollow valve.

FIG. 3 is a central vertical sectional front view showing that the lower end of a punch is in contact with the upper end of material when a ram moves down.

FIG. 4 is a central vertical sectional front view showing that the lower end of a center pin invades in the lower part of a blind hole in the material when the ram further moves down.

FIG. 5 is a central vertical sectional front view showing that the material is forged when the ram moves down to the lower limit.

FIG. 6 is a central vertical sectional front view showing that the lower end of the center pin leaves a cavity of the primary intermediate when the ram moves up slightly.

FIG. 7 is a central vertical sectional front view of a second press for molding a secondary intermediate of the hollow valve.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

One embodiment of the present invention will be described with respect to drawings.

FIG. 1 (a) to (e) show the steps in order with respect to a method of producing a hollow valve according to the present invention, in which (a) is material of the hollow valve, (b) is the step for molding a primary intermediate of the hollow valve, (c) is the step for molding a secondary intermediate, (d) is the step for inserting metallic sodium 4 into the secondary intermediate, and (e) is the step for closing an opening of the secondary intermediate 3 with a closure 5.

A long circular rod with martensite or austenite steel is cut to a predetermined length to form the material 1 in which a blind hole 6 is formed at a center with a drill. The blind hole 6 comprises a smaller-diameter hole 6 a at the bottom, and a larger-diameter hole 6 c which communicates with the smaller-diameter hole 6 a via a taper hole 6 b. The larger-diameter hole 6 c is approximately twice as large as the smaller-diameter hole 6 a in an internal diameter.

The primary intermediate 2 in FIG. 1( b) is molded by forward hot extrusion of the material 1 with a first press 7 or friction press in FIG. 2.

The first press 7 comprises a die 9 fixed by a die holder (not shown) and having a shaping hole 8 at a center, and an elevatable cylindrical ram 10 above the die 9. The shaping hole 8 comprises a larger-diameter portion 8 a which is approximately equal to an external diameter of the material 1 and is open at the top; a squeezing portion 8 b which tapers downward and communicates with the larger-diameter portion 8 a; and a smaller-diameter portion 8 c which communicates with the lower end of the squeezing portion 8 b and is open at the bottom of the die 9.

A cylindrical punch holder 11 which is coaxial with the shaping hole 8 of the die 9 fits in the lower part of the ram 10 and moves vertically. In the punch holder 11, a larger-diameter portion 12 a of the punch 12 fits in the punch holder 11 and does not move vertically. A smaller-diameter portion 12 b of the punch 12 has an external diameter which is approximately equal to an internal diameter of the larger-diameter portion 8 a of the die 9 and can fit in the larger-diameter portion 8 a.

At the center of the punch 12, there are formed a larger-diameter guide hole 13 a and a smaller-diameter guide hole 13 b for guiding a center pin 17 vertically.

On the punch holder 11 in the ram 10, a lower surface of a cylindrical spring retainer 14 is in contact with an upper surface of the punch holder 1, and the spring retainer 14 slides vertically. In the spring retainer 14, a compression spring 15 is disposed. An upper surface of the compression spring 15 is in contact with a lower surface of a spring tap 16 which fits in the upper end of the ram 10 to prevent the compression spring 15 from getting out upward.

The spring retainer 14 is spaced from the spring tap 16 so that the compression spring 15 can be compressed by the spring tap 16.

In the larger-diameter guide hole 13 a and the smaller-diameter guide hole 13 b of the punch 12, an upper larger-diameter portion 17 a and a lower smaller-diameter portion 17 b are in sliding contact. An external diameter of the smaller-diameter portion 17 b is approximately equal to an internal diameter of the larger-diameter hole 6 c of the material 1 and the larger-diameter portion 8 of the die 9 so that the smaller-diameter portion 17 b fits in the larger-diameter hole 6 c and the larger-diameter portion 8.

From the ram 10 above the die 9, the smaller-diameter portion 17 b projects downward at a predetermined length. The larger-diameter portion 17 a is spaced from the lower end of the larger-diameter guide hole 13 a so that the center pin 17 moves vertically at a predetermined stroke.

The upper end of the larger-diameter portion 17 a of the center pin 17 is in sliding contact with the guide hole 18 at the center of a bottom wall 14 a of the spring retainer 14.

Within the compression spring 15, a cylindrical spacer 19 engages at its upper end in a recess 20 at the lower surface of the spring tap 16 and engages at its lower end on the upper end of the center pin 17.

The center pin 17 is fixed to the spring tap 16 by engaging the lower end of a bolt 21 which is inserted downward in the spring tap 16.

At the lower end of the smaller-diameter portion 17 b of the center pin 17 projecting from the lower end of the punch 12, a smallest-diameter portion 24 is provided via a taper portion 23. In order to prevent the smallest-diameter portion 24 from cutting off, the smallest-diameter portion 24 is formed at the lower end.

The external diameters of the taper portion 23 and the smallest-diameter portion 24 are slightly smaller than the internal diameters of a squeezing portion 8 b and a smaller portion 8 c. When the ram 10 and the center pin 17 are disposed at the lowest position, an annular gap is formed between the outer circumferential surfaces of the taper portion 23 and the smallest-diameter portion 24 and the inner circumferential surfaces of the squeezing portion 8 b and the smaller-diameter portion 8 c in FIG. 5.

FIGS. 2-6 illustrate the steps for molding the primary intermediate 2 by the first press 7.

In FIG. 2, after the ram 10 rises, the material 1 heated to a predetermined temperature is inserted in the larger-diameter hole 8 a of the shaping hole 8 in the die 9, and the ram 10 moves down. In FIG. 3, the lower end of the punch 12 comes in contact with the upper end of the material 1, and the taper portion 23 and the smallest-diameter portion 24 at the lower end of the center pin 17 gets in the blind hole 6.

The ram 10 further goes down. In FIG. 4, the spring tap 16 compresses the compression spring 15 and moves down. Before the compression spring 15 is compressed, the material 1 is not pushed by the punch 12, and only the center pin 17 integrally formed with the ram 10 further moves down, so that the lower end of the center pin 17 moves into a position close to the lower end of the blind hole 6 of the material 1. Meanwhile, spring force by the compression spring 15 exerts on the punch 12, so that the material 1 is strongly pressed by the lower end of the punch 12.

The ram 10 further moves down to the lowest position. In FIG. 5, the material 1 is pushed out downward from the punch 12. The taper portion 23 of the center pin 17 moves down close to the squeezing portion 8 b. The smaller-diameter portion 24 stops at a position where it moves down by the length of the smallest-diameter portion 24 from the upper end of the smaller-diameter portion 8 c.

Thus, the material 1 plastically flows into the smaller-diameter portion 8 c through the squeezing portion 8 b of the shaping hole 8 to form a solid section 2 c at the lower part of the stem 2 a. The material 1 is prevented by the lower end of the center pin 17 from flowing to the axis; passes through the annular gap between the outer circumferential surfaces of the taper portion 23 and the smallest portion 24 and the inner circumferential surfaces of the squeezing portion 8 b and the smaller-diameter portion 8 c; and is pushed out into the smaller hole 8 c of the shaping hole 8, so that a cavity 25 is formed in the stem 2 a on the solid portion 2 c.

By the series of extruding steps, in FIG. 1( b), the primary intermediate 2 which has a head 2 b at the upper end of the stem 2 a is molded. By the projection of the smaller-diameter stem 17 b of the center pin 17 from the lower end of the punch 12, a broader hole 26 which communicates with the cavity 25 is formed. The thickness of the stem 2 a in which the cavity 25 is formed is approximately equal to the gap between the outer circumferential surface of the smallest-diameter portion 24 and the inner circumferential surface of the smaller-diameter hole 8 c.

In FIG. 6, after the primary intermediate 2 is molded, the center pin 17 moves up with the ram 10. During a little upward motion, the punch 12 is forced by the compression spring 15, so that the primary intermediate 2 is pressed downward by the lower end of the punch 12. Thus, at the same time with upward motion of the ram 10, the taper portion 23 and the smallest-diameter portion 24 of the center pin 17 can easily be pulled out of the cavity 25 in the head 2 b and the stem 2 a.

The ram 10 is elevated to the upper limit and the lower end of the stem 2 a of the primary intermediate 2 is pushed up by an eject pin (not shown). Thus, the primary intermediate 2 thus molded can be taken out of the die 9.

FIG. 7 illustrates a second press 27 for molding the secondary intermediate 3 in FIG. 1( c). A second die 31 fits in a recess 30 at the upper end of a die holder 29 in which a through hole 28 which is larger in diameter than the stem 2 a of the primary intermediate 2 is formed at the center. The second die 31 has a second shaping hole 32 gradually spreading in diameter upward, and an axial hole 33 which communicates with a through hole 28 in the die holder 29. The second press 27 is disposed near the first press 7 side by side. With a single friction press apparatus, the primary intermediate 2 and the secondary intermediate 3 can be molded by the first press 7 and the second press 27 respectively at the same time.

A second punch 37 fits in a recess 35 in a second ram 34. A projection 36 on the second punch 37 approximately conforms with a shaping hole 32 of the second die 31. By contacting the upper surface of the second die 31 with the lower surface of the second punch 37, a space for molding a head of a hollow valve is formed between the second shaping hole 32 and the projection 36.

In order to mold the secondary intermediate 3, while the second ram 34 moves up to the upper limit, the primary intermediate 2 is pulled out of the die 9 and is immediately put into the second die 31 to allow the second ram 34 to move down to the lower limit. The head 2 b of the primary intermediate 2 is plastically deformed by the lower surface of the punch 37 and the projection 36, thereby molding the secondary intermediate 3 with a head 3 b at the upper end of a stem 3 a in FIG. 1( c). A hole 38 is formed in the head 3 b to communicate with the cavity 25 in the stem 3 a.

After the secondary intermediate 3 which is taken out of the second press 27 is heated, metallic sodium for cooling the valve is inserted into the cavity 25 in the stem 3 a in FIG. 1( d).

After metallic sodium is inserted into the cavity 25 in the stem 3 a, a closure 5 fits in an opening of the hole 38 in the head 3 b of the secondary intermediate 3. The closure 5 is fixed by a welding device (not shown) to close the opening of the hole 38. Thus, a hollow valve 39 with the hollow head 3 b and hollow stem 3 a is obtained. The hollow valve 39 thus made is finished and machined with a cotter groove at the axial end.

As described above, according to a method of producing a hollow valve in the foregoing embodiment, in order to create the cavity, it is not necessary to pull a core out or to bore with a gun drill conventionally, but the cavity 25 can readily be created in the stem 2 a simultaneously with molding of the primary intermediate 2 by extruding the material 1, so that a hollow valve can readily be manufactured at low cost efficiently.

The cavity 25 in the primary intermediate 2 can also be used as a guide hole for a drill. Without necessity of creating a cavity in a stem with a gun drill first, boring can readily be made for a short time thereby improving productivity and prolonging its life with reduced load to the drill.

Furthermore, when the head 2 b of the primary intermediate 2 is molded to the secondary intermediate 3 by forging, the cavity 38 is formed in the head 3 b to lighten the whole valve. By increasing heat-radiation area on a valve including metallic sodium, the head 3 b can be cooled efficiently.

The cavity 38 in the head 3 b gradually increases in diameter upward thereby facilitating the operation for inserting metallic sodium 4 into the head 25.

The present invention is not limited to the foregoing embodiment.

In the foregoing method, the blind hole 6 was already formed in the material 1. While the lower end of the center pin 17 is inserted into the blind hole 6, the material 1 is strongly pressed with the punch 12 to flow downward plastically.

The material 1 may be a solid cylinder. The upper surface of the solid material 1 is strongly pressed and plastically deformed by the lower end of a center pin 17 having a longer projection than in the foregoing embodiment. A bottom hole is formed at the center of the material by putting the projection of the center pin into the material. The lower end of the pin lowers until it puts down into the upper end of a smaller hole thereby molding the primary intermediate.

The step for forming the bottom hole in the material formerly can be omitted.

In the foregoing producing method, after the secondary intermediate 3 is molded, metallic sodium 4 for cooling the valve is inserted into the cavity 25 in the stem 3 a. In order to lighten a valve only, the step for inserting metallic sodium may be omitted.

In the foregoing apparatus, the punch 12 and the center pin 17 rises and lowers with the ram 10 in the first press as friction press. For example, a punch and a center pin may independently rises and lowers with a time lag by two hydraulic presses. Only a punch may be elevated by a friction press and a center pin may be elevated by a hydraulic press with a time lag. Thus, a compression spring may be omitted. By setting elevation timing of a center pin to a punch properly, introduction time of a smallest portion into a smaller hole of a shaping hole may be optimum or the lower end of a center pin may readily be pulled out through cavities in a primary intermediate.

The foregoing merely relates to embodiments of the invention. Various changes and modifications may be made by those skilled in the art without departing from the scope of claims wherein: 

1. A method of producing a hollow poppet valve, the method comprising: forming material that has a blind hole which is open at an upper end; pressing the material in a shaping hole in a die strongly to allow the material to pass through a downward-tapered squeezing portion of the shaping hole to extrude the material into a smaller-diameter portion of the shaping hole; and moving a pin down to allow the lower end of the pin to invade into an upper end of the smaller portion of the shaping hole to allow the material to plastically flow through an annular gap between an outer circumferential surface of a lower end of the pin and an inner circumferential surface of the smaller-diameter portion of the shaping hole thereby molding a primary intermediate of the valve, the primary intermediate comprising a stem and a larger-diameter head at an upper end of the stem, the primary intermediate having a cavity that has an opening at an upper end of the head.
 2. The method of claim 1 wherein the lower end of the pin is moved down to a lower end of the blind hole of the material before the material is strongly pressed by the punch.
 3. The method of claim 1 wherein the pin is elevated after the primary intermediate is molded while the upper end of the primary intermediate is pressed by the punch.
 4. The method of claim 1, further comprising forging the head of the primary intermediate to mold a secondary intermediate which comprises a stem, a head and a cavity; and closing the opening of the head with a closure.
 5. The method of claim 4 wherein metallic sodium is inserted into the cavity in the stem through the opening of the head, before the opening of the head is closed with the closure.
 6. The method of claim 4 wherein the hole in the head of the secondary intermediate gradually increases in diameter upward.
 7. A method of producing a hollow poppet valve, the method comprising: pressing a cylindrical material disposed in a shaping hole in a die, with a pin strongly to deform the material plastically to move a lower end of the pin into the material to form a blind hole having an opening at a top along an axis of the material; pressing the material strongly to allow the material to pass through a squeezing hole which tapers downward of the shaping hole to exclude the material toward a smaller-diameter portion of the shaping hole; and allowing the material to plastically flow downward through an annular gap between an outer circumferential surface of a lower end of the pin and an inner circumferential surface of the smaller-diameter portion of the shaping hole to mold a primary intermediate which comprises a stem and a larger-diameter head at an upper end of the stem, the primary intermediate having a cavity that has an opening at an upper end.
 8. The method of claim 7 wherein the pin is elevated after the primary intermediate is molded while the upper end of the primary intermediate is pressed by the punch.
 9. The method of claim 7, further comprising forging the head of the primary intermediate to mold a secondary intermediate which comprises a stem, a head and a cavity; and closing the opening of the head with a closure.
 10. The method of claim 9 wherein metallic sodium is inserted into the cavity in the stem through the opening of the head, before the opening of the head is closed with the closure.
 11. The method of claim 7 wherein the hole in the head of the secondary intermediate gradually increases in diameter upward.
 12. An apparatus for producing a hollow poppet valve, the apparatus comprising a first press that comprises: a die having a shaping hole that comprises a larger-diameter portion into which material can be inserted, a squeezing portion which communicates with the larger-diameter portion and tapers downward, and a smaller-diameter portion which communicates with the squeezing portion to form a stem of the poppet valve; a ram that rises and lowers above the die; a punch attached to the ram, a lower end of the punch being capable of moving into the larger-diameter portion of the shaping hole in the die; and a pin disposed to move up and down in a vertical guide hole along an axis of the punch and connected to the ram, a smallest portion at a lower end projecting from the punch downward to put into the smaller-diameter portion of the shaping hole.
 13. The apparatus of claim 12, further comprising pressing means for forcing the punch downward to press the primary intermediate downward until the pin moves up.
 14. The apparatus of claim 13 wherein the pressing means comprise a compression spring.
 15. The apparatus of claim 12, further comprising a second press disposed near the first press, the second press comprising: a die holder; a ram above the die holder to rise and lower; a die in a recess in the die holder having a shaping hole; and a punch in a recess in the ram and having a projection at a lower end, the head of the primary intermediate being forged and molded between the projection of the punch and the shaping hole of the die by the second press to form a head of the secondary intermediate of the hollow poppet valve. 